Osteoporosis is developed due to the disruption of the balance between the functions of osteoblasts responsible for bone formation and osteoclasts responsible for bone resorption. Compounds that activate osteoblasts and the other compounds that inhibit osteoclasts are considered to be effective for the treatment of osteoporosis. Estrogen may activate osteoblasts and inhibit osteoclasts and has been used in the treatment of osteoporosis. However, it also acts on cells other than bone, particularly, on reproductive organs. Therefore, there is concern about side effects such as increased risks of uterine cancer and breast cancer. Moreover, the Ministry of Health, Labour and Welfare issued safety information dated Jan. 29, 2004 alerting people that the long-term estrogen medication might increase a chance of the onset of breast cancer or dementia. Furthermore, the synthesis of estrogen is complicated and difficult because of its complex molecular structure.
Melatonin (N-acetyl-5-methoxytryptamine) having an indole skeleton has been reported to act in an inhibitory manner on both osteoblasts and osteoclasts (Non-Patent Document 1). However, there has been no report about the relationship between a tryptophan derivative and its effect on osteoblasts and osteoclasts.
Non-Patent Document 1: N. Suzuki and A. Hattori, J. Pineal Res., 33, 253-258 (2002)